The present invention relates to an image forming apparatus which reproduces a halftone image by a modulation signal which has been modulated according to a reference signal, and more particularly relates to an image forming apparatus which modulates image density data.
Technique disclosed in U.S. Pat. No. 4,847,641 has been well known as an example of prior art which is applied to a mapped binary image data. In the aforementioned technique, a matching table is utilized to the targeted edge portion so that the image density and image position by a pixel in the targeted edge portion can be redistributed.
However, when an image of high quality is processed, the image data becomes a multi-value image, so that the situation is different from the aforementioned binary image. That is, in the case of a multi-value image, halftone density information exists in a targeted pixel. Furthermore, the amount of information about the matching table becomes large, so that the cost of the apparatus is raised and it is difficult to process image data at a high speed.